The inner surface of a pneumatic tire is typically comprised of an elastomeric composition designed to prevent or retard the permeation of air and moisture into the carcass from the tire's inner air chamber. It is often referred to as an innerliner. Rubbers, such as halobutyl and blends of butyl and halobutyl rubber, which are relatively impermeable to air are often used as a major proportion of the innerliners.
Accordingly, the air and moisture permeability resistance of the innerliner rubber composition is an important consideration.
The innerliner is normally prepared by conventional calendering or milling techniques to form a strip of uncured compounded rubber of appropriate width which is sometimes referred to as a gum strip. Typically, the gum strip is the first element of the tire applied to a tire building drum, over and around which the remainder of the tire is built. When the tire is cured, the innerliner becomes an integral, co-cured, part of the tire. Tire innerliners and their methods of preparation are well known to those having skill in such art.
There remains an ongoing desire to provide enhanced or suitable variations of butyl rubber-based tire innerliners without significantly affecting the air and moisture permeability resistance of the innerliner rubber composition.
Halobutyl and butyl rubbers are usually one of the most expensive elastomers used in a tire. Given the competitive tire market and the continued need to lower the cost of manufacturing tires, there exists a desire to decrease the cost of innerliners which perform such an important function in the performance of a tire.
In the description of the invention, the term “phr” relates to parts by weight of a particular ingredient per 100 parts by weight of rubber contained in a rubber composition. The terms “rubber” and “elastomer” are used interchangeably unless otherwise indicated, the terms “cure” and vulcanize” may be used interchangeably unless otherwise indicated and the terms “rubber composition” and “rubber compound” may be used interchangeably unless otherwise indicated. The term “corncob granules” is used herein to refer to corncob granules which are obtained from the woody ring surrounding the central core, or pith, of the corncob. The corncob granules are manufactured by drying the woody ring portion, or fraction, of the corncob followed by grinding to produce the granules which are air cleaned and separated into various sizes by mesh screening. Such corncob granules are manufactured by The Andersons, Inc. and sold as Grit-O' cobs® (corncob granules, for example as 60 Grit-O' cobs®. For further corncob granule discussion, see “Use of Fine-R-Cobs as a Filler For Plastics”, by D. B. Vanderhooven and J. G. Moore, reprinted from the Internal Wire and Cable Symposium 1982.